1. Field of the Invention
The present invention relates to a liquid crystal display device, and particularly, a structure of a pixel including a liquid crystal and a backlight.
2. Description of the Related Art
A liquid crystal display device is formed by a combination of a liquid crystal panel in which a liquid crystal is sandwiched between a pair of substrates and a lighting system called a backlight on a rear side of the liquid crystal panel. As for the liquid crystal panel, a simple matrix mode and an active matrix mode using a thin film transistor (TFT) are known (refer to Patent Document 1: Japanese Published Patent Application No. H9-90404). In either mode, a voltage which is applied to electrodes sandwiching the liquid crystal is controlled, and the quantity of transmitted light of the backlight which illuminates the entire surface of the liquid crystal panel is adjusted, whereby an image is displayed. Therefore, for example, also in a case of black display in all the pixels, the backlight is always turned on and the power is kept being consumed.
Meanwhile, a liquid crystal display device using a light-emitting diode (LED) as a backlight is provided. The LED has advantages such as the long lifetime, no need of an inverter since it can be directly driven by a low-voltage direct current power source, low power consumption, and the like. As for such a backlight, a directly-below type and a sidelight type are known as a position of the LED. In a directly-below type, the LED is positioned directly below the liquid crystal panel, and the LED emits light uniformly on the surface using a diffusing plate or the like. In addition, in a sidelight type, the LED emits light from the side surface of the panel, and the light is supplied to the liquid crystal panel through a light-guiding plate or a diffusing plate; thus, the sidelight type can be formed thinly compared to a directly-below type, which is an advantage.